The present invention is directed generally to fiber optic devices, and more particularly to single and dual-fiber collimators utilizing polarization-maintaining fibers.
In the field of fiber optic communications, information is transmitted optically over a network of single-mode or multi-mode fibers. Many of the switching and splitting functions in these networks are accomplished in free space, where the light may exit the fiber and interact with active and/or passive optical components. In some instances, it may be necessary to collimate the optical beam exiting the fiber for efficient interaction with the external components. Also, the transmitter unit in fiber optic communication systems is typically a semiconductor laser diode, which has a linearly polarized output which may be coupled to a polarization-maintaining fiber.
When preparing a break in an optical communication link, it is common to insert the exposed fiber optic into an optical ferrule for protection of the delicate glass fiber. There are applications where it may be desirable to have two or more such fibers in the same ferrule transmitting and/or receiving at different optical wavelengths, or at the same wavelength.
Given the above, there is a need for an optical collimating device incorporating a multi-port ferrule which can accommodate an input optical signal carried by a polarization maintaining fiber.
Generally, the present invention relates to a fiber collimator device that includes polarization controlling optics to simplify the manufacture of fiber collimators that use polarization maintaining fiber. In particular, the use of the polarization control optics in a fiber collimator reduces the need to align the polarization axis of the polarization maintaining fiber, thus reducing the time spent on fabricating the device.
In particular, one embodiment of the invention is directed to a fiber collimator unit having a first focusing element having an optical axis and a first focal length. A first optical fiber is optically coupled to a first side of the first focusing element, and is disposed at a first transverse distance from the optical axis so that light from the first optical fiber propagates on a second side of the first focusing element as a substantially collimated beam at a first angle to the optical axis. A first polarization rotator is disposed on the second side of the first focusing element. The polarization rotator deviates the polarization state of the substantially collimated beam. There is an optical element that substantially redirects light at a first pre-determined polarization state and substantially transmits light at a second pre-determined polarization state orthogonal to the first polarization state.
Another embodiment of the invention is directed to a method of aligning light in a fiber optic device. The method includes transmitting a first polarized light from a first port disposed towards a first end of the device through a polarization rotator and adjusting the polarization of the first output light to a selected state by rotating the polarization rotator. The method also includes reflecting light in the selected polarization state back so that the reflected light propagates through the polarization rotator to a second port disposed towards the first end of the device.
Another embodiment of the invention is directed to an optical system that has an optical transmitter producing output light, an optical receiver receiving at least a portion of the output light, and an optical fiber link coupling between the optical transmitter and the optical receiver. At least two light sources have outputs combined in fiber device having a first focusing element having an optical axis and a first focal length. A first optical fiber is optically coupled to a first side of the first focusing element. The first optical fiber is disposed at a first transverse distance from the optical axis so that light from the first optical fiber propagates on a second side of the first focusing element as a substantially collimated beam at a first angle to the optical axis. A first polarization rotator is disposed on the second side of the first focusing element, the polarization rotator deviating the polarization state of the substantially collimated beam. An optical element substantially reflects light at a first pre-determined polarization state and substantially transmits light at a second pre-determined polarization state orthogonal to the first polarization state. An output form the fiber device is coupled into the fiber link.
The above summary of the present invention is not intended to describe each illustrated embodiment or every implementation of the present invention. The figures and the detailed description which follow more particularly exemplify these embodiments.